A carrier aggregation (CA) technology allows user equipment (UE) to simultaneously use multiple component carriers (CC) to perform uplink and downlink communication, and implements high-speed data transmission. In addition, the CA technology enables multiple base stations to simultaneously undertake transmission of a data service of user equipment. UE that is in a coverage area shared by multiple adjacent base stations may aggregate cells provided by the multiple base stations, so that the multiple base stations simultaneously undertake transmission of the data service of the user equipment. During this process, data synchronization between the UE and the multiple base stations is required.
For a process in which UE accesses a base station, specific implementation of the CA technology is as follows: the UE obtains timing advance TA (TA) for initial uplink sending by performing random access to the base station, and then the base station continuously adjusts uplink sending of the UE according to a time at which uplink data is received. During a process of random access, the UE sends one preamble (preamble) to the base station, where the preamble sent by the UE in a cell is calculated according to a cell identity and a parameter that is included in a broadcast message. 64 available preambles exist in one cell and are classified into two types: a dedicated preamble and a public preamble. The dedicated preamble is allocated by a base station for use and the public preamble is selected by UE for use. After determining to initiate random access, the UE randomly selects one preamble from a public preamble resource pool and sends the preamble to the base station. If the UE needs to transmit uplink data, the UE selects one preamble and initiates contention-based random access; if the base station needs to transmit downlink data, the base station selects one dedicated preamble for the UE, informs the UE of the dedicated preamble, and instructs the UE to initiate random access, where because the preamble is dedicated, there is no conflict between the UE and another UE, and the random access is referred to as non-contention based random access.
The prior art is specific to carrier aggregation for a cell of a single base station, however, in a carrier aggregation scenario in which there are multiple base stations, how to implement random access among user equipment and different base stations is a problem expected to be resolved in the industry.